An E-Mail conversation between myself and Jason Werner concerning light weight hingelines that took place on the GSAL mailing list on 5-24-00

-----Original Message-----
From: maillist@gsal.org [mailto:maillist@gsal.org]On
Behalf Of Branwell McClory
Sent: Wednesday, May 24, 2000 8:38 AM
To: GSAL GSAL;
Subject: Weight loss idea for hinge wood.

Hi All,

Today's thought on making a plane lighter.

One of the components that weigh quite a lot on a
large plane, is the hinge wood.

Here is an idea to address it.

Your basic hinge wood setup goes like this.
You have a thick sheet of balsa that runs the length
of the surface.
You bevel it and add slots for the hinges.

The end result is that you have a solid "V" shape bit
of wood that runs the length of the surface.

How about this.

Example:
The rudder of a 35% Cap.

Take a 3/32 sheet of balsa instead of the usual 1"
thick piece and glue it where the usual hinge wood
would be.
Next, take the standard hinge wood, bevel it and then
cut out 4 x 1.5" sections. One section per hinge.
Take these sections and laminate 1/64 ply across the
sides so it can't split and slot them for the hinges.
Glue these "V" sections to the 3/32 part in the place
the hinges normally go.
In the void between these "V" sections, glue in a
upright of 3/32 balsa.

Now, when covered, it will look like a standard hinge
line but in reality, it will only have wood where it
is needed, not where it isn't.

Branwell

// Reply from Jason Werner

Branwell,
 
Good idea...I think.  But the problem is surface area vs strength of wood.  I think a better idea would be the following:
 
- replace the last 1 in of white foam with "blue" or dense foam. Glue on before sheeting and shape.  This will include a bevel for the normal hinge gap seal.  Total weight change on a 30 in piece will be +1 oz or less.
 
- again, before sheeting set in the hinge "blocks"
into the blue and white foam.  Bevel them to match the bevel in the
foam. 
 
- Again, before sheeting take 2 layers of 1.7 oz Kevlar cloth cut on a 45 degree bias.  Using epoxy (very little) lay the Kevlar over the "v" and back about 1 inch over the blue foam.  The overlap can be minimal, but is necessary.  Use Mylar sheets to get a good smooth finish on the epoxy/Kevlar (you can even pre-paint it!).
 
- bag/sheet the wing as normal.

The Kevlar will keep the whole "surface" from coming apart under load.  The 45-degree bias helps with torsional loads as well as increasing the total strength.  The weight of 2 layers + epoxy is well under the weight of a single piece of balsa.  The blue foam is there for a similar reason...it is slightly stronger than the white foam used at a VERY minimal weight gain.  I would say that you could lose several ounces of total weight on a wing and 1-2 oz on a tail surface.  Not hard to do either <G.  End result should be stronger than the original as well!

Other advantage - Another advantage is the ability to do total gapless hinge surfaces.  Similar to Peter G's Cap with the curved section.  Foam is VERY easy to shape with a hot wire and templates, so a male/female hinge line would be easy to do.  The Kevlar (or even fiberglass) is done before the wing is sheeted, so any "mistakes" are hidden.  Once sheeted, the wing is simply cut apart along the hinge line and trimmed to
allow full freedom of movement.  Would be kind of nice.

Want me to do it on the wings?

Jason

// Reply from Branwell

Hi Jason,

I like the CC hinge idea and would be willing to give
it a shot except......
What would one use for hinges ?.

I have thought of using the CC thing before but the
only hinge solution I came up with was to use DuBro
hinge points embedded in aluminum tubes.

Easy enough but I have not found hinge points to be a
reference on longevity, if you know what I mean.

As to the blue foam and Kevlar, good idea, you have
the go ahead.
The only thing to remember is that the ailerons need
to be 4" from the center of the hinge line to the
trailing edge and the full span of the wing.
They should also be split, 80% outboard and 20%
inboard with both sections capable of 45 degrees up
and down movement.

Any ideas on the hinges ?.

Branwell

// Reply from Jason

Branwell,
Robart hinge points, what else <G?  The hinge "line" is offset slightly towards the center of the C on the control surface.  This design actually helps mass balance the surface some because of hte forward weight
of the surface.
But for the super lightweight one lets just try standard V hinges. I will go ahead and make them for ya.  I personally would use quite a few Hinge Points, but you can specify the # and type and I will go ahead with
that.

BTW - for whose of you wondering how to vac bag a "V" in the sheeting (or how am I going to do this at all <G).  The setup is actually quite easy.
 
-We first cut the core alond hte "hinge" line and add in a section of blue foam.  Attach the blue foam with 3M-77 is fine, as the bond is not that critical between the foams.
 
-The wing is now "whole" again and is sanded/planed down to it's original shape.  The core looks like white/blue stripe/white .

-The LE and TE pieces are now attached and planed down to the surface (little trick to hold it all straight.
 
-Next a "template" is added to the tip and root to guide a hot wire in making the hinge bevel in the foam.
 
- Go ahead and cut the bevel, top and bottom.  Remember to add wire kerf as well as skin thickness.  SAVE the extra pieces!!!!!!!

- Sand the bevel down perfect.
 
- Make the cutouts for the hinge blocks.  Go ahead and glue in the pre-drilled hinge blocks into the wing.  Plane and sand flush.
 
- On the 45 degree bevel pieces go ahead and glue a strip of 14mil Mylar onto each "bevel" side.  This will fit into the "v" when bagging.  Wax the Mylar for release later.
 
- Ready to bag?  make the sheeting. 
 
- Cut 2 strips of Kevlar on the 45 degree bias.  About 3 in wide is enough.  Just has to overhand the top and bottom skin by a little.
 
- Attach the Kevlar with a light coat of 3m-77 to the Bevel.
 
- Bag the wing with the following differences:
  
- Using a foam roller wet out the Kevlar...really well!!!
  
- Wet out the sheeting.
  
- Attach the foam core to the sheeting, followed by the bevel, and finally the aileron (or control surface).
  
- Attach the top piece and bevel.
  
- Secure with a bit of tape put in bag using cores (outside the bag) as alignment.

-Pull the vac.  Make sure to realign and tighten up the cores to prevent pulling down.
 
-Once cured, you can cut through the bevel piece to remove the core.
Slice the skin flush with the Kevlar and peel away the Mylar.  It should only require a bit of touchup to be perfect.
 
- Slice the Kevlar away from the hinge holes and you are done.

Jason